Corrosion inhibiting lubricating composition



United States Patent Otfice 2,991,251 Patented July 4, 1961 coRRosroN invention relates to materials and methods for in. hrbitmg the lead corroding tendency of compositions contarmng partial esters of aliphatic polyhydroxy alcohols. lfarmcularly, it relates to oil compositions comprising partlal esters of polyhydroxy alcohols and minor amounts, sufiicient to inhibit lead corrosion, of mercaptobenzothiazole or its derivatives and/or hydroxy benzoic acid or its derivatives.

Fatty acid partial esters of aliphatic polyhydric alcohols, e.g., sorbitan monooleate, have found widespread use for inhibiting the corrosion of iron. However, in certain applications where the composition containing the partial ester also comes in contact with lead, the partial ester causes excessive corrosion of lead, even though inhibiting the corrosion of iron. For example, mineral oil compositions containing sorbitan monooleate have been used 1n the crankcase of piston-type aircraft engines to prevent rusting during storage. For this use, the engine is run for a short period of time to circulate the composition through the engine, after which the engine is turned off, and the oil drains back to the crankcase, leaving a protective film on the cylinder walls and other internal parts of the engine. Recently, for purposes of economy, it has become desirable to use the same composition for actual operation of the engine, rather than to remove the rust preventive oil composition and replace it with fresh lubricating oil. However, when the oil composition containing the partial ester was later used as lubricating oil, such that the composition was circulated through the engine for long periods of time, excessive corrosion of the lead in the copper-lead hearings in the engine occurred. It has now been found that the lead corroding tendencies of these partial esters may be effectively curbed, Without interfering with their rust inhibiting properties, by the addition of a minor amount of mercaptobenzothiazole and its derivatives, or hydroxy benzoic acid and its derivatives.

The compositions of the invention will generally comprise an oil base, about 1 to 25, e.g., 2 to weight percent of the partial ester, and about 0.01 to 2.0, e.g., 0.03 to 1.0 weight percent of the lead corrosion inhibiting material.

The oil base will generally be a mineral lubricating oil, although other petroleum bases such as kerosene, gas oil, naphthas, petrolatum, etc. may be used.

The partial esters used as rust preventives include the C to C fatty acid partial esters of aliphatic polyhydric,

alcohols having about 3 to 12, e.g., 3 to 8 carbon atoms, and about 2 to 8, e.g., 3 to 6 hydroxy groups per molecule. Preferred materials are the monoand diesters of C to C alcohols having about 3 to 6 hydroxyl groups and prepared from C to C fatty acids. The above type of partial esters includes the partial esters of the monodehydrated aliphatic polyhydric alcohols, which are well known in the art, for example, see US, Patent 2,434,490, as well as partial esters of non-dehydrated aliphatic polyhydric alcohols, e.g. pentaerythritol monooleate.

Specific examples of the above types of partial esters will therefore include: glyceryl monooleate, pentaerythritol monooleate, sorbitan monooleate, the dioleates of sorbitan, mannitan, pentaerythritol and related polyhydric alcohols, the corresponding partial stearic and palmitic acid esters of these alcohols, and partial esters of these alcohols made from mixtures of these fatty acids.

' The lead corrosion inhibiting agents are organic mate rials containing an aromatic nucleus, and are oftwo general types as follows:

Mercaptobenzothiazoles and its derivatives having the general formula:

wherein each R is hydrogen or a C to C e.g., C to C alkyl group. Specific examples of such materials include: Z-mercaptobenzothiazole; Z-mercapto, 4,6-dimethyl benzothiazole; Z-mercapto, 4-methyl, 6-octyl benzothiazole; 2- mercapto, 4-tertiary butyl benz-othiazole; etc.

Salicylic acid and its derivatives having the general formula:

COOH

wherein R is hydrogen or a C to C straight or branchedchain alkyl group.

Specific examples of the salicylic acid materials of the above formulas include: salicylic acid, 2-hydroxy-3 methyl bcnzoic acid, 2-hydroxy-4 octyl benzoic acid, etc.

Other additivematerials, to adapt the composition of :the invention to special applications, may also be included in the composition in amounts of about 0.05 to 10.0 wt. percent based on the weight of the total composition. -For example, it may be desirable to add other rust preventive additives, such as petroleum sulfonates and, lecithin; viscosity index improvers, such as polymethacrylates and polyisobutylene; oxidation inhibitors; etc. Materials of increased consistency may also be prepared by thickening the oil composition of the invention with appropriate soaps, polymers, waxes, etc. In some cases, the addition of a C to C e.g. C to C alkyl amine to the composition seems to aid in inhibiting lead corrosion, particularly when it is used in conjunction with the salicylic acid type inhibitor. The lead corrosion inhibitors of the invention were found to be the only effective materials of a wide number of similar type materials and other known inhibiting agents which were tested. This is shown by the following examplea: t

. EXAMPLE I The test for lead corrosion was the S.O.D. lead corrosion test, which was carried out by suspending rotating copper and lead strips for one hour in the oil composition maintained at a temperature of 325 F. Following this, the lead strip was removed and the change in Weight of the strip, in terms of milligrams per square inch of strip, was measured. The above test was carried 3 sults of this series of tests are summarized in the following table:

Table I S.0.D. LEAD CORROSION TEST [1 hour at 325 F. with copper catalyst} Wt. Percent Inhibitor Added to Oil-Sorbitan Mono- Lead Strip oleate Composition Weight Loss (mg/sq. in.)

011, per se 6 95% oil and sorbitan monooleate 249 1.0 Ditcrtiary butyl para cresol 231 1.0 Phenyl alpha naphthylarninc 262 1.0 Hydroquinone rnonomethyl ether- 308 1.0 Lecithin 395 1.0 Amine irom hydrogenated tallow acid 194 0.5 Z-Ethyl heiryl amine 195 1.0 adduct of salicylaldehyde and ethylene diamine 361 0.5 Dioctyl phosphoric acid 268 0.5 'lrioctyl p n p 187 0.5 Zinc dioctyl dithiophosphate 278 1.0 Cetyl mercaptan 312 0.5 Tridodccyl borate 308 0.5 Methyl thluram disulfide 207 1,0 Phenothiavinp 199 1,0 Mercaptnhpnmthiamln +4 0.1 Mercaptobenzcthiazole 132 EXAMPLE II Another series of compositions was tested by adding various inhibitors to the oil-sorbitan monooleate composition of Example I. However, in these tests the lead strip was exposed for two hours at 325 F. and no copper was present. Results are reported in Table H.

Table 11 MODIFIED S.O.D. LEAD CORROSION TEST [2 hrs. at 325 F. without copper catalyst] Weight Loss Wt. Percent Inhibitor Added to Oil-sorbltan Monoof Lead oleate Composition Test Strip (mg/sq. in.)

95% oil and 5% sorbltan monooleate 121 0.1 Salicylic a 0.05 Salicylic acid 100 0.1 Salicylic acid+0.1 n-butyl amine. .0... 5 0.05 Salicylic acid+0 .05 n-butyl .amlne- 101 0.1 Salicylic acld+0.05 mercaptobenzothiazole- 0 .05 Salicylic acid+0.05 mercaptobenzothiazole.

As seen from Table II, the lead corrosiveness of the oil-sorbitan monooleate composition was somewhat less in the absence of the copper catalyst (cf. Table 'I) 'The salicylic acid per se was very efiective in inhibiting the lead corrosion. The addition of 0.1% alkyl amine with the 0.1% salicylic acid was also found very effective,

as are blends of salicylic acid and mercaptobenzothiazole. The use of aliphatic hydroxy acids such as citric, maleic and tartaric acids was not effective.

The inhibitors of the invention can also be mixed directly with the partial ester or concentrates thereof to form a rust preventive additive mixture which is also inhibited against lead corrosion.

To further illustrate the invention, other compositions can be prepared as follows:

A. 0.05 wt. percent of 4-methyl, 6-n-octy1 benzothiazole can be added by simple mixing to a composition consisting of 1.0 wt. percent of glyceryl monostearate and 99.0 wt. percent of mineral lubricating oil of the type used in Example I.

B. 2.0 wt. percent of 2-hydroxy-4-n-octyl benzoic acid can be added by simple mixing to a composition consisting of 10.0 wt. percent of the dioleate of mannitan and 90.0 wt. percent of mineral lubricating oil of the type used in Example I.

C. 5 wt. percent of mercaptobenzothiazole may be mixed with 95 wt. percent of Span 80 (sorbitan monooleate) to form an additive mixture.

In summary, the invention relates to materials and methods for inhibiting the lead corroding tendencies of compositions containing a fatty acid partial ester (usually the monoor diester) of a polyhydric alcohol by mixing into said compositions about 2 to 40 wt. percent, e.g. 4 to 20 wt. percent, based on the weight of partial ester, a lead corrosion inhibitor. This lead corrosion inhibitor may be mercaptobenzothiazole, or its ring substituted alkyl derivatives or salicylic acid or its ring substituted alkyl derivatives or mixtures thereof.

What is claimed is:

1. A lubricating composition which is rust preventive and substantially non-corrosive to lead, which comprises a major proportion of mineral lubricating oil, about 1 to 25 wt. percent of sorbitan monooleate, and about .03 to 1.0 wt. percent of a material selected from the group consisting of mercaptobenzothiazole, salicylic acid, and mixtures thereof.

2. The lubricating composition of claim 1, wherein said material is mercaptobenzothiazole.

3. The lubricating composition of claim 1, wherein said material is salicylic acid.

4. The lubricating composition of claim 1 which also contains 0.5 to 10.0 wt. percent of a C to C alkyl amine.

5. A lubricating composition which is rust preventive and substantially non-corrosive to lead, comprising a major amount of mineral lubricating oil, about 2 to 10 wt. percent of sorbitan monooleate, and about 0.03 to 1.0 wt. percent of a material selected from the group consisting of mercaptobenzothiazole and salicylic acid.

References Cited in the file of this patent UNITED STATES PATENTS Schiermeir Sept. 20, 1949 

1. A LUBRICATING COMPOSITION WHICH IS RUST PREVENTIVE AND SUBSTANTIALLY NON-CORROSIVE TO LEAD, WHICH COMPRISES A MAJOR PROPORTION OF MINERAL LUBRICATING OIL, ABOUT 1 TO 25 WT. PERCENT OF SORBITAN MONOOLEATE, AND ABOUT .03 TO 1.0 WT. PERCENT OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF MERCAPTOBENZOTHIAZOLE, SALICYLIC ACID, AND MIXTURES THEREOF. 